when early to mid-season fruit develops, because soil is cooler and plants have fewer roots

during fruit set, and tomatoes need calcium to bind together cells

when watering is inconsistent

when temperatures are excessive – either too cold or too hot – which interferes with water uptake

when season starts out wet and turns dry during fruit set, just as tomatoes need calcium the most

when plants are grown in cold, heavy soil which prevents roots from developing strong

when soil has excessive salts, which reduce calcium availability

How can you control and treat blossom end rot?

Prevention is the most method of control (see below).

Blossom end rot cannot be reversed on a tomato once it’s set in, but you can take these steps to slow and halt it.

Amend soil with source of calcium and water in prior to seasonal planting.

Pick affected fruit to reduce stress on the plant and allow it to direct its energy to other tomatoes.

Cut out spots on harvested fruit and eat remainder. Blossom end rot does not make the rest of the tomato inedible. However, if tomatoes have been infected by fungi or mold, discard them.

How can you prevent blossom end rot?

There are lots of ways you can take precautions for next year’s crop!

Carefully harden off young seedlings gradually to protect them from extreme temperatures and conditions.

Select a planting area with good drainage.

Avoid setting out plants too early in the season, which can expose them to cold temperatures and cold soil. Allow soil to warm before planting.

Work in plenty of compost and organic matter into the soil before planting, so that the plant’s root system has a better chance to grow strong and deep.

Add quick-release lime when planting tomatoes so that there’s plenty of calcium in the soil and it’s absorbed quickly. Tomatoes grow best when the soil pH is about 6.5.

Keep your tomatoes’ water supply even throughout the season so that calcium uptake is regular. Tomatoes need 1-3 inches of water a week. They perform best when watered deeply a couple of times a week rather than superficially every day.

Determinate tomato varieties are more prone to BER because they set fruit in a short period of time. Indeterminates and semi-determinates set fruit throughout the season, making it easier for plants to regulate calcium intake.